#my_name: Yan Zihao(Mike)
#my_email: 1752041815@qq.com

while True:
    #用num1变量存输入的数
    num1 = input("Please enter a number: ").strip()
    #判断输入的是不是证书
    if not num1.isdigit():
        print("输入无效,请重新输入")
        continue
    num2 = int(num1)
    #判断输入的数是不是5的倍数
    if num2 == 0:
        print(f"{num2} is not a multiple of 5.")
    elif num2 % 5 == 0:
        print(f"{num2} is a multiple of 5.")
        break
    else:
        print(f"{num2} is not a multiple of 5.")
